Free/DelftShip to Rhino - a direct method.

Discussion in 'Software' started by rwatson, Aug 11, 2013.

  1. rwatson
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    rwatson Senior Member

    Long story - because that's what you want right ? This might help a few budding CADders.

    The boat concept was first developed in Freeship, to take advantage of its statistical reports, to get the 'statics right. Then , to build a scale model, the strategy used to get the CNC frame lines, was to use the plan, side and front elevations from Freeship ( the LinesPlan ), read into Autocad, and then use 2d Autocad to project the frame profiles onto a 2d environment. The problem is, in Freeship you can specify how many stations ( and you need to use as many stations as will give the best detail in the design), but you cant selectively create station profiles for where you want to have a mould placed for building from.

    This conversion seemed to work OK, but some little niggles I found in the model build made me curious.

    I took the frame files used for the CNC cutting, and loaded them into Rhino, and added chine lines. You could see the 'wonky bits' very easily. When I applied the FAIR command to the chine and sheer lines, they left the vertical station lines by a noticeable margin. Not a big deal in a small model, but disaster in a full size.

    So, the mission was to get a totally accurate takeoff from the original 'X'-ship file.

    The export and import into Rhino as a 3d DXF mesh went ok, but Rhino cant manipulate meshes very well. It was easy to convert the meshes into a PolySurface, and join them all together.

    Then, following advice from several places, including help on this forum, I put 'intersecting surfaces' at the desired station distances.

    The big puzzle was how to 'extrapolate' the 'junction' between the two surfaces.

    The key command was IntersectTwoSets - that produces a curve that can then be manipulated as desired, including producing a frame CNC cutting profile.

    I have included a screenshot form Rhino to illustrate the process.

    It would probably be easier to use the Marine add on for Rhino in future, but for budget development, this may be useful for some people.
     

    Attached Files:

  2. lewisboats
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    lewisboats Obsessed Member

    I was always able to get station profiles when exporting the offsets. Each station is defined in the offset file.
     
  3. rwatson
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    rwatson Senior Member

    Yes, thats what I have done too. But, to re-type all that data from the offset text file, into points to create a cutting file for CNC machines, is a very tedious affair, if you can get all the stations you want, and not some at odd, non uniform positions.

    I would be interested to hear of other ways around the problem, for sure.
     
  4. bhnautika
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    bhnautika Senior Member

    Warning! The above method may be ok for flat surfaces but using mesh-based surfaces for section lines on curved surfaces has its problems. It is precision sensitive on the export side and when turned into a poly surface to get section lines they are not a continuous curve but a number of curves/arcs between end points. Picture shows section through round bilge boat, dark blue line is from surface from freeship 2.6 in iges format. Light blue section is mesh dxf converted to polysurface then sectioned. The pair on the left the most obvious were exported at medium precision the right at high. As can be seen the high precision is better but it is the same as the left just closer. This may or may not be a problem but its good to know.
     

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  5. rwatson
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    rwatson Senior Member

    Thanks BKN. That is useful to know. I have just been inspecting the curves produced, and have found some anomalies as you predicted. (attached). I would have been tearing my hair out if you hadnt warned me,

    is there an alternative approach that produces better results that you have come across ?
     

    Attached Files:

  6. rwatson
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    rwatson Senior Member

    Out of interest, I superimposed the manually produced frame line (Purple) (via Autocad) with the 'derived from Polysurface ' line result (Yellow), and got this result. (attached)

    The slightly more concave hull side ( intentional ), but a small anomaly where the sheerline becomes a cabin top ( .09 m )

    An interesting thing, when the IntersectTwoSets command was started, it came up with a message that there was a gap in the lines at the sheerline of less than something,something, and asked if I wanted to join it ( I said yes )

    Overall though, the accuracy was visually acceptable, but you would need to clean up the line to put it through a CNC router.
     

    Attached Files:

  7. bhnautika
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    bhnautika Senior Member

    It’s the problem of using meshes rather than a continuous surface like “nurbs”. What other export options do you have.
     
  8. rwatson
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    rwatson Senior Member

    ah, good point.

    Freeship has 2d and 3d Polylines or IGES.

    Are these preferable ?
     
  9. bhnautika
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    bhnautika Senior Member

    iges would be my choice with the highest precision.
     
  10. rwatson
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    rwatson Senior Member

    Tried the Export3d Polylines.

    Although the import results in a whole set of individual Poly lines as the drawing, when I place an extruded plane across the multiple lines, the IntersectTwoSets command produces a curve at the intersections, which I would never have expected.

    I can also place individual points at the intersections if I wanted to plot a frame, which I cant do with a Polysurface.

    There is a discontinuity at the same location, but nowhere near as bad as the converted surface method
     

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  11. bhnautika
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    bhnautika Senior Member

    why rebuild the surfaces in rhino when you have them in freeship?export the surfaces using iges.
     
  12. jarmo.hakkinen
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    jarmo.hakkinen Junior Member

    If I understood You correctly, You are trying to get CNC-routing files from Free!Ship -lines plan. Well, after modelling in FS, with as many stations as necessary for best control on the shape desired, delete these stations, and create a new set of them at the spacing of the building moulds. If the spacing is uneven, they have to be added one by one. And if You wish to have them milled in 5-axis router, add a station on both fore- and aft-sides of a mould. (Tools->Intersections->Add one station). Check the highest precision, and export the lines plan.

    In Rhino or Autocad, You now have the station outside lines with both fore and aft sides of a frame. Create the inside of a frame with for example offset-tool. Move one of the station faces "upwards (positive z)" the thickness of a frame, and create surfaces all around the frame. (In the lines plan, everything is on the same x-y plane). That's it, if modeled to the moulded dimensions, otherwise use "Offset face" to reduce planking thickness.

    If not using lines plan, but exporting as 3D-polylines, the procedure is much the same, only the fore-and-aft station lines of a frame are already at correct distance, no need to move anything "upwards". Just create the inside lines of a frame, add surfaces around and offset face if necessary for the planking.

    Jarmo
     
  13. rwatson
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    rwatson Senior Member

    Great info there. I had never come across that technique in Free/Delft ship

    Luckily, I dont need to to worry about the height of the cuts in a 3.5 D router, but that might be useful sometime in the future

    Not sure about that info. If you have the time and/or inclination, please feel free to expand on that concept.


    BNK
    "why rebuild the surfaces in rhino when you have them in freeship?export the surfaces using iges. "

    The aim was not to get the surfaces, but to get the frame profiles to manipulate CNC cuts in moulds. Exporting direct to CNC router isnt an option, as there is lots of manipulation to do to the cutting files - nesting being the least of the work.

    I just tried the IGES format, and it is more accurate. It identified the 'problem spot' where the designer in Freeship looks like they tried to do something tricky with the decks.

    Basically, Free/Delftship are such pigs of software to use for anything but the most basic designs, that I would rather not use them at all. The little kerfuffle with the deck/sheerline in this file is a classic example. Impossible to spot, and a real pig to fix. In Rhino, its not a problem.

    I emailed some ORCA3 sellers today, to get prices for the marine add-ons for Rhino, but I am scared of the answer. Double the price of Rhino !!!

    Thanks for the handholding guys, I am learning lots.
     
  14. jarmo.hakkinen
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    jarmo.hakkinen Junior Member

    Frames: Freeship to Rhino

    Explaining the procedure with my limited English is more easily done with some screenshots, so I made up the attachment. Rwatson, the "correct distance" I meant, is the thickness of the frame, whose bow and stern outer edges are defined by the stations spaced by the thickness, so, in dxf-3d-polylines, they are already in right positions, as can be seen on pages 2-3 of the attachment. No need to move them as is the case with 2d- lines plan. Hope this clarifies things a bit.

    Now, some coffee.

    Jarmo
     

    Attached Files:


  15. DCockey
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    DCockey Senior Member

    If the hull shape is going to be imported into Rhino or re-created in Rhino, then why not obtain the frame shapes in Rhino rather than in FreeShip?
     
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